The thermal rating of an insulation system describes the quantitative relation of life of an insulation system to the temperature and time of exposure. The end of life is defined by the mechanical/electrical loss of integrity of the insulation system after exposure. A Temperature Index (TI) is then assigned based on temperatures and times recorded during the test. It should be noted that the Index is based upon the time at which 50% of the samples have failed. A related quantity is Relative Temperature Index (RTI) and is obtained when a candidate insulation system is simultaneously tested with a known insulation system using identical conditions (e.g., same temperatures, time intervals, and oven). RTI has been found to be more meaningful than TI since it is less affected by the variations in test conditions and procedures.
Also included in this document is an extensive appendix to assist the user in performing and interpreting this test. Included in the appendix is an example which provides greater detail for those who have not previously run this test. This type of detail is not included in any of the referenced documents.
This test method serves several purposes. Initial qualification of new aerospace wires to specifications for both commercial and military users may be established by using the TI and RTI. Also, it provides engineering information data for assigning operating or rating temperatures for a specific insulated wire.
The high temperature test may be used to statistically compare the thermal performance data of a lot of wire with the original test data. The high temperature test is not recommended for use in continuing production quality control procedures until empirical evidence shows that the high temperature test or another analytical procedure, such as a thermogravemetric test, can accurately provide quality control testing information.